These studies seek to assess the effects of environmental agents on spermatogenesis, sperm maturation, functions of accessory organs, and male reproductive capacity. Mechanisms of toxicity are studied, and new approaches to toxicity testing are proposed and validated in order to extrapolate more reliably from laboratory animals to man and to improve our ability to analyze risk. The following studies are in process: (1) to define the biochemical nature of the molecules of epididymal monoclonal antibodies, the site of action, and the origin of sperm surface glycoproteins; (2) the study of the functional role of the sperm surface molecules and the identification of environmental chemicals which perturb these molecular processes; and (3) mechanisms by which environmental chemicals modify gene expressions of male reproductive organs.